Cellular networks such as Code Division Multiple Access (CDMA), Universal Mobile Telecommunications System (UMTS) and Long Term Evolution (LTE) use the hierarchical structure. For example, in the CDMA2000 Radio Access Network (RAN), multiple Mobile Stations (MSs) connect to a Base Station (BTS); multiple BTSs connect to a Base Station Controller (BSC) and Packet Control Function (PCF) which typically are collocated at Radio Network Controller (RNC); multiple RNCs connect to a Packet Data Serving Node (PDSN). The PDSN serves as the gateway from the RAN to the rest of the packet network. When Mobile IP (MIP) is used, the MIP Foreign Agent (FA) is located on the PDSN and all traffic associated with a MS will be tunneled between the FA and the MIP Home Agent (HA). For authentication, authorization and accounting (AAA) purposes, the RNC connects to the AAA server for the access network, which is called an Access Network-AAA (AN-AAA), and the HA connects to the AAA server for the entire network. FIG. 1 graphically illustrates the hierarchy of network elements in an exemplary CDMA2000 RAN, as discussed above.
In deployed (i.e., real life) cellular networks, typically not all network elements are located in the same central office (CO). In fact, because of geographic considerations and the need to provide load balancing and fault tolerance between elements in the hierarchically designed network, RNCs are typically connected to PDSNs located in different central offices across wide area networks (WAN). Similarly, PDSNs are typically connected to Home Agents located in different central offices across WAN. It is also possible for AN-AAAs and RNCs to be residing in different offices and for AAAs and Home Agents to be located in different offices.
FIG. 2 depicts an illustrative portions of a network in which CDMA2000 network elements are distributed across two central offices A and B. Any connection between network elements beyond an RNC needs to cross the WAN between the central offices. Given the configuration of FIG. 2, all of the interface traffic must pass through access routers (R) connecting the central offices. As a result, the following interfaces between network elements all contribute to inter-office WAN traffic:                A10 interface for data and A11 interface for signaling between RNC and PDSN,        A12 interface between RCN and AN-AAA,        A13 interface between Home Agent and AAA, and        IP-in-IP tunneling traffic for Mobile IP between PDSN and Home Agent.        
As 3G data service becomes increasingly popular, wireless service providers (WSPs) experience increased inter-office traffic load and the consequent bandwidth requirements for inter-office traffic increase.